Prisoners tense after whip's fixed (8)
I believe the answer is:
constant
'fixed' is the definition.
(I've seen this in another clue)
'prisoners tense after whip's' is the wordplay.
'prisoners' becomes 'cons' (short for convicts).
'tense' becomes 't' (abbreviation used in many dictionaries).
'after' says to put letters next to each other.
'whip' becomes 'tan' (I've seen this in another clue).
't' after 'tan' is 'tant'.
'cons'+'tant'='CONSTANT'
(Other definitions for constant that I've seen before include "exactly as before" , "Loyal - firm" , "Persistent and unchanging" , "staying the same" , "Steadfast or unvarying" .)